Drawer interlock (devices permitting only one drawer of a stack of drawers to be opened at one time) are by no means new to the furniture industry but most prior art devices, including applicant's own prior art structures, are relatively complex to manufacture and time consuming to install. In general, the more complex the structure, the more noisy is the apparatus and the more chance there is for failure of a single component and the consequent failure of the interlock.
Closest know approaches in the prior art, to the interlocks herein, are found in the U.S. Pat. No. 3,941,441 of Douglas Scheerhorn and in the U.S. Pat. No. 4,889,396 of Terry L. Mitchell, et al. The Scheerhorn device employs a continuous cable operating by reason of slack left in the cable.
In the Scheerhorn device, upon the opening of one drawer, the other drawers are blocked by a taking up of slack in the cable. The interlock mechanisms of Scheerhorn comprise a single rotary cam adjacent to each drawer. The cable travels or runs in a segmented guide. When a drawer is opened, the cam in the open space between guide segments is activated by a catch and the catch, in moving the cam, takes up all of the available slack in the cable. Thus the cam element removes the slack and the slack is held so as to block the removal of any other drawer or drawers consequent to the lack of slack. The cam structure of Scheerhorn is complex and the installation of the cam construction requires very careful attention at assembly and placement within the cabinet served by the drawers.
The prior art of Terry L. Mitchell, et al., (supra) depends upon the movement of segmented vertically moveable elements and their manipulation and blocking or releasing of the drawer elements by their new position through intermediate cam movement.
The present device utilizes a constantly tensioned relatively non-yielding element, preferably a web strap acted upon by a slider element and the slider element responding to a separate rotary cam and the slider movement acting against a spring induced tension blocked by a rigid physical barrier and the consequence is a more positive interlock and a far simpler structure to manufacture, install and integrate with modern stacked drawer systems so that only a single drawer can be opened at a time and the entire stack limitedly resists displacement at all times and is easily locked by physical blocking of the tensioned element as by a simple key structure acting on a blocker arm.
The resultant construction of the present invention is less expensive to build, easier to install, and substantially indestructible in normal usage. The versatility and flexibility of the present invention is a substantial forward and unobvious step in drawer interlock construction.
The interlock device of Scheerhorn utilizes a slack cable and the single rotary cam requires substantial vertical space to be activated at opening of a drawer to make the slack cable taut and, in doing so, provides an uneasy rather than positive, blocking of the tendency with the cable to resist and return the rotary cam to its initial position. The consequence of the geometry of a rotating cam is to limit the movement of the cable to the difference between the length of the cord and the length of the arc created by the radius of the cam.
By contrast the present invention utilizes a compact cam thereby serving drawers of minimal depth and acts to positively shift a rectangular faced slider, first against a taut spring resistance force and after the cam turns substantially beyond ninety degrees (90.degree.) the tension force against the slider by the strap toggles against the slider in an over-center relation. The cam holds the slider in place until the drawer is closed. The relative simplicity and positive locking of the construction of the present invention lends the device to functioning in a simple channel, such as steel, to preassembly and to installation in any file cabinet or stack of drawers as a complete module easily controlled by conventional lock means interfering positively with the spring in prevention of opening any drawer in the stack until the conventional lock enables the spring to perform.
The implications of the present improved structure are readily recognizable as the description proceeds by those who are familiar with the requirements and installational limits in furniture such as file cabinets, desk drawer pedestals and the like.